听力文本

This vast forest circling the globe contains a third of all the trees on Earth
这片环绕着地球的广大森林容纳了地球上1/3的树木
and produces so much oxygen it changes the composition of the atmosphere.
产生了大量氧气，从而改变了大气成分
As we travel south so the sun's influence grows stronger
随着我们向南行进，太阳的影响力逐渐增强
and at 50 degrees of latitude a radical transformation begins.
北纬50°的地方是一场重大变革的起点
Summers here are long enough for broadleaf trees to replace conifers.
由于有足够长的夏季，阔叶林得以取代针叶林
Broadleaves are much easier to eat and digest
阔叶树的树叶更容易食用和消化
so now animals can collect their share of the energy that has come from the sun.
因此动物们也能获得太阳馈赠给它们的那部分能量

It's summer and these forests are bustling with life.
现在是夏天，森林中一片生机勃勃的景象
But the good times will not last.
可是好景不长
Broad leaves must be shed in winter for their damage by frost.
由于严寒的原因，阔叶树得在冬天落叶
As they disappear, so the land becomes barren with little for animals to eat.
树叶消失之后，大地一片荒凉，动物们的食物日益稀少
The inhabitants must migrate, hibernate, or face months of near starvation.
居民们只得迁往他处，或者冬眠，或者忍受几个月的饥荒

词汇解析

1.the composition of ...的成分
But the composition of that investment is tilting toward government securities.
但这些投资的成分，却正在向政府债券倾斜。

2.bustling with life 生机勃勃
The university is bustling with life.
这所大学充满生机。

3.months of 数月的
Gray worked for him in the early months of his campaign for some time, then became disillusioned, freaked out and joined another party.
格雷在他竞选的头几个月曾为他工作过一段时间，后来幻想破灭而很快加入了另一方。

视频及简介

北极的春季，北极熊妈妈和它的孩子从它们的洞穴中走出来，它们只有短短的两周时间，它们要在冰雪融化前穿越冰冻的大海，它们进退两难。在这集中，我们将看到一些最难得的、完整的北极熊生活的画面。